Metopic suture is a dense fibrous joint extending from the nasion to the bregma. Normally, closure of this suture takes place between 1-8 years of age. Failure of this closure beyond 8 years leads to persistent metopic suture. A rare case of persistent metopic suture in a 60-year-old male is documented, who committed suicide by alleged consumption of organophosphorous compound at District Govt. Wenlock Hospital, Mangalore, Karnataka, India. Metopic suture may mimic skull fracture and may mislead an inexperienced forensic expert. Neurosurgeon should also be aware of this anatomical variation while performing frontal craniotomy, as the persistent metopic suture may mimic vertical fracture of the skull. Hence, in this case report, the clinical and medico-legal implications of the persistent metopic sutures have been discussed.

In the recent years, variations of cranial sutures are commonly studied because of their significance in various fields of medicine and surgery. Metopic suture is a dense connective tissue extending from the nasion to the bregma. The fusion of this metopic suture starts at the anterior fontanelle and terminates at the nasion. [1]

Fusion of suture between the two frontal bones occurs at the age of (1-3) years. [2] But, earlier studies have shown that the age of fusion varies from as early as 1 year to 7 years, the upper limit might extend upto 8 years. [3] Failure to fuse leads to persistent metopic suture above the age of 8 years. [4] Racial variations in the incidence of fusion of metopic sutures and shapes have been observed. [5] Caffey claimed that metopic suture may persist up to the sixth year and even throughout life in about 10% of cases in dry skull studies. [6]

Case Report

Medico-legal autopsy was conducted on the dead body of a 60-year-old male at District Govt. Wenlock Hospital, Mangalore after receiving authorization from the investigating officer.

Autopsy findings

External Examination: Dead body of an elderly male, wheatish in complexion, moderately built and nourished, weighing 65 kg and measuring 163 cm in length. No evidence of external injuries over the body. There was no evidence of head injury.

Routine reflection of the scalp tissue revealed a midline vertical suture extending from nasion to bregma over the frontal bone suggestive of persistent frontal suture.[Dentate suture] [Figure 1],[Figure 2],[Figure 3]. The posterior part of the persistent frontal suture is the pars bregmatica, and this area is included within the anterior fontanelle. The anterior end of the frontal suture fails to meet the suture between the two nasal bones. The coronal and the sagittal sutures were normal in appearance [Figure 1].

The incidence of the metopism and difference in shapes varies by races. [5] It is also called median frontal suture, usually present between the two superciliary arches. [7] Sometimes, there may be presence of wormian bones. [8] In a recent study conducted in South India, metopism was observed in 3.2% of the skulls, and incomplete metopic suture was present in 26.4% of the 125 adult skulls that were examined. [9] 2.66% of adult Indian skulls have metopic suture. [1]

Various theories have been proposed for the persistence of metopic suture. Active expression of some of the cytokines during cranial fusion can be one of the causes. [10] Another study has mentioned that active resorption of the chondriodal tissue results in metopism. [11] If it does not disappear, it may be called a "metopic suture" or "sutura frontalis persistens." If it is a premature closure, it will cause a keel-shaped deformity of the skull called trigonocephaly.

Medico-legal and surgical importance

Persistent metopic suture may mimic vertical fissure fracture of skull, which leads to wrong interpretation by an inexperienced medical officers performing medico-legal autopsies or interpreting skull X-rays. Persistent metopic suture can be diagnosed by x-ray of the skull AP view. To avoid wrong diagnosis in emergency conditions, 2D and 3D CT scans are strongly recommended. Multiplanar reformat of CT scans also give valuable information about shape, [12] extent, and closuring status of metopic suture. [13] Hence, the neurosurgeons should be aware of this anatomical variation while performing frontal craniotomy. The autopsy surgeons should be updated with anatomical entity of persistent frontal suture while differentiating it from midline fissure fracture of the skull.